把网页的图片保存到iphone应用作为背景，速度太慢了

我在网上找到了把网页的图片保存到应用作为背景的方法，就是速度太慢了。

10kb的图片如果一张还可以，如果有15-20张，就像卡住了似的。有没有什么方法可以让从网上直接下载图片速度快一些？图片是批量下载的。而且还能保持图片质量。

define kBgQueue dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0) //1

import "downloadImage.h"

@interface downloadImage ()

@end

@implementation downloadImage

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {

    }
    return self;
}



- (void)viewDidLoad
{
    [super viewDidLoad];

    NSString *imgUrl = @"http://somesite.com/someimage.jpg";

    dispatch_async(kBgQueue, ^{

        [self performSelectorOnMainThread:@selector(downloadImageFromWeb:) withObject:imgUrl waitUntilDone:YES];

    });

}

-(void)downloadImageFromWeb:(NSString *)imgUrl{


    UIImage *image = [[UIImage alloc] initWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:imgUrl]]];

    NSArray *parts = [imgUrl componentsSeparatedByString:@"/"];

    NSString *imgFilename = [parts lastObject];

    [self saveImage:image:imgFilename];

}


- (void)saveImage:(UIImage*)image:(NSString*)imageName {

    NSData *imageData = UIImageJPEGRepresentation(image, 100);
    NSFileManager *fileManager = [NSFileManager defaultManager];

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];

    NSString *fullPath = [documentsDirectory stringByAppendingPathComponent:
                          imageName];

    [fileManager createFileAtPath:fullPath contents:imageData attributes:nil];



}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];

}

@end